This invention relates to sheet fed, off-set rotary printing presses of the type having a one and one half to one delivery system, and more particularly to a new and improved transfer device for use in the delivery system of such presses.
In a sheet fed, off-set rotary printing press, it is necessary that the wet ink side of a freshly printed sheet be supported during transfer of the sheet from the press impression cylinder to either a press delivery station or to another printing station within the press. To effect the transfer from the impression cylinder, most off-set printing presses employ a delivery system which includes a chain conveyor carrying a gripper bar assembly having sheet grippers which grip the leading edge of the sheet and pull the sheet from the impression cylinder around a transfer device which typically includes skeleton wheels, drums, cylinders or other support members depending upon the type of press involved, which support the wet ink side of the sheet during the transfer.
With rotary presses having a one to one delivery system where the transfer device rotates one complete revolution during each passage of a gripper bar assembly, it has been found that a delivery system using the inventions described in U.S. Pat. Nos. 3,791,644 and 4,402,267 issued, respectively Feb. 12, 1974 and Sept. 6, 1983, to Howard W. DeMoore, can be reliably and effectively used to support the wet ink side of the printed sheet with out marking or marring the sheet. The inventions described in the foregoing DeMoore patents have received wide acceptance in the printing industry and have achieved very substantial commercial success, and transfer and delivery systems embodying those inventions are currently being manufactured and sold under license by Printing Research, Inc. of Dallas, Texas, the assignee of the present invention. Each of the foregoing patents, the disclosure of which are hereby incorporated herein by this reference, employs a wheel or drum formed as a cylinder having a cylindrical sheet support surface which is discontinuous and formed with a single longitudinally extending opening to permit the gripper bar assembly to pass around the wheel or drum adjacent the impression cylinder.
Prior to the present invention, it was not thought possible to use a wheel or drum type device such as disclosed in the above identified DeMoore patents in a rotary press employing a one and one half to one delivery system, since the transfer wheel or drum must rotate one and one half complete revolutions for each passage of a gripper bar assembly, and to provide two longitudinal openings along the drum of a size sufficient to permit the gripper bar assembly to pass through the nip between the impression cylinder and the transfer device would reduce the effective support surface of the transfer device below that required for effective sheet support without marking. Accordingly, prior to the present invention rotary presses using a one and one half to one delivery system have typically used skeleton wheels of the general types referred to as prior art in the DeMoore U.S. Pat. No. 3,791,644. Such prior art skeleton wheels typically comprise thin disc shaped wheels having a fluted or serrated rim designed to provide minimum surface area contact with the wet inked surface of the freshly printed sheet, and which typically are adjusted along their drive shaft so as to engage the sheet in an area where minimum wet ink is present. In a press having a one and one half to one delivery system, the prior art skeleton wheels are segmented so as to form two openings between rim segments to permit the gripper bar assemblies to pass around the wheel adjacent the impression cylinder.
One problem inherent in the use of prior art skeleton wheels in a one and one half to one delivery system is that the press must be stopped and the position of the skeleton wheel adjusted for each new print job being run. Further, unless the prior art skeleton wheels can be located to engage the sheet only where no wet ink is present, for example in the margins of a page, the rim of the skeleton wheel may mark or mar the printed sheet and leave "tracks" and indentations on the printed sheet.
Another problem which has been encountered with the delivery system of such a press is that the effective diameter and speed of rotation of the transfer device must be the same as those of the impression cylinder so that there will be no relative motion between the sheet leaving the impression cylinder and engaging the support surface of the transfer device. In presses having a one and one half to one delivery system, the transfer device is typically chain driven, and it is extremely difficult, if not impossible to maintain the rotational speed of the transfer device equal to that of the impression cylinder. As a result, it has been found that relative motion between the sheet and the support surface of the transfer device has caused marking and marring of the wet ink surface of the sheet.
Thus, there exists a need for a new and improved transfer device for use with the transfer or delivery system of a press having a one and one half to one delivery system which will permit the prior art skeleton wheels used with such presses to be replaced with a wheel or drum type system which can take advantage of the inventions disclosed in the above mentioned DeMoore patents so as to substantially prevent marking and marring of the printed sheet. As will become more apparent from the following, the present invention solves this need in a new and unobvious way.